The present invention relates generally, as indicated, to a method for on-line fluid injection into and/or removal from freshly extruded material preferably on a continuous basis as such material is extruded.
As used herein "extrude" means to force, press, push out, shape, or the like, a material by forcing the same through a die. An "extruder" or an "extruding machine" means an apparatus for performing the act of extruding. Moreover, "extrusion" means an article or material produced by the use of an extruder, and a "fresh extrusion" means an extrusion that has just been extruded. "Green strength" means the strength of a relatively fresh extrusion including the ability of the latter to maintain its extruded shape. "Fluid" is used in its generic sense to mean either a liquid or gas or other material that has fluid-like properties, e.g. capable of flowing, although as will be described further the preferred embodiment effects gas injection or removal.
To assure that a fresh extrusion has sufficient green strength, for example to hold its shape until finally cured, dried, fired, or otherwise finished, relatively close control of the formulations of ingredient materials, e.g. particulate matter, water, clay, and other materials, to an extruder, the rate of extruding, the pressures and temperatures used, etc. usually require relatively close control. With a too small green strength a fresh extrusion may lose its desired shape or in extreme cases could disintegrate. The use of extruding techniques to form shaped solids from particulate material ingredients or the like is usually substantially more efficient than casting techniques. Extruding generally is performed on a continuous basis, thus maximizing the efficiency of the equipment, labor, and often power requirements; whereas casting of particulate material ingredients to form a solid thereof is performed on a batch basis in which plural mixing, pouring, molding, removing, cleaning, and like operations must be individually and relatively inefficiently performed.
One material that may be extruded or cast is clay, which may be categorized either as a quasi-particulate or as a quasi-fluid material often having a property that tends to resist change of shape. Thus, a clay extrusion or casting usually will hold its shape relatively well. On the other hand, particulate materials, such as coal fines, metal mill scale, BOF dust and the like usually require the addition of a binder thereto to hold the many particles in fixed relation to retain a given extruded or cast shape. One such binder used in the past has been an asphalt type or petroleum-base type binder. However, such binders often are relatively slow in their curing, hardening, catalyzing, or solidifying characteristics, such terms being used generally synonymously herein. Such property, on the one hand, makes those binders useful in extruding, for the materials in the extruder ordinarily will not harden and damage the extruder or require substantial down time for cleaning in case the extruder encounters a brief failure causing shut down. On the other hand, though, such property reduces the efficiency of extruders, which would have to be operated at a sufficiently slow rate to assure that the fresh extrusion has a sufficient green strength to hold its shape.
Two part binders have been used in casting techniques. A typical two part binder includes, for example, a resin or like material, such as formaldehyde, vinyl, epoxy, or the like, and a catalyst, such as an amine, peroxide, or other hardener, respectively, for causing a solidication of formaldehyde, vinyl, or epoxy. In one casting technique using such two part binder, the particulate matter, and both ingredients of the binder, for example the epoxy and its catalyst, was thoroughly mixed and placed in a mold until the epoxy had cured to form the solid casting. Thereafter, the solid casting was removed from the mold, which would be cleaned and prepared for the next casting. However, in the past the use of such premixture of a two part binder, especially a fast curing one, in extruding processes could destroy the extruder or substantially damage the same requiring cleaning and/or repair if the extruder were to shut down briefly allowing the material therein to harden in situ. In another casting technique, known as the Acme process, particulate matter and one part, say the resin or epoxy, of a two part binder was mixed and the mixture placed in a mold. The mold was closed and the catalyst was injected under pressure to cause the batch of material therein to harden forming the solidified casting. In the second technique a closed mold was necessary to receive and to confine the injected catalyst, but such enclosure was not available with continuously operating extruders.